The use of OLED panels as a lighting device is desirable—such as for area lighting in the workplace and the home. The OLED lighting device has characteristics that are different than an OLED display and these differences can be exploited to improve reliability and ease of manufacture while reducing cost. For example, electrical shorts are a major concern with OLED devices. A short occurs when any imperfection in the OLED causes its cathode to be in direct contact (or very close proximity) with its anode resulting in an area of much lower resistance than the remaining area between the anode and the cathode. Shorts may occur in any of the layers forming the element and may be caused by, for example, substrate imperfections or asperities, anode layer irregularities, non-uniformity of the one or more organic layers, and airborne particles introduced in the element structure during handling. While a pixel failure due to a short in an OLED display renders the display useless, a failure of a strip in the OLED lighting device may be acceptable as long as the resulting output luminance is not significantly deteriorated.
Furthermore, the OLED lighting device has to be significantly cheaper than an OLED display. Therefore, cost and yield considerations dictate that the OLED lighting devices are not manufactured such that electrical shorts are completely eliminated, thus, the lighting device should be manufactured to be fault tolerant. To make the OLED lighting device fault tolerant, either the anode or the cathode is separated into strips. In this case, if one of the strips has a short during device operation, then the shorted strip can be switched off without significantly deteriorating the output luminance of the lighting device. By switching off the shorted strip, the possibility of the entire lighting device failing is avoided. A fuse can be used to switch off a strip by significantly decreasing current flow through it when a large current flows through the fuse due to the short. Typically, a fuse is externally attached to each of the strips (i.e., a fuse is externally attached if it is not on the substrate) and because the fuses are externally attached, each of the strips requires an external contact. Manufacturing the lighting device with the external contacts for each strip is cumbersome. Also, external fuses also increase the complexity of the driver circuitry and the complexity of the connection components (e.g., the contact pad and the flex connector).
For the foregoing reasons, it is desirable to have electroluminescent lighting devices that exploit its unique characteristics to improve device reliability and efficiency while minimizing cost.